Browsing by Author "Fikru Lealem"

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    Amylase Production by Bacillus Species Isolated from Fermenting Tef and Kocho
    (Addis Ababa University, 1993-06) Fikru Lealem; A.Gashe Berhanu (PhD)
    Amylase producing bacterial strains associated with kocho and tef fermentation were isolated. The strain from fermenting kocho was identified as Bacillus subtilis while the strain from fermenting tef was identified as Bacillus licheniformis. Conditions for the productions of amylases were investigated. The bacterial strains secreted amylase into a liquid medium containing 1% soluble starch. When starch was replaced by disaccharide and monosaccharide, amylase production was reduced. Amylase production was higher with unfermented kocho compared to other native straches. Of the nitrogen sources tested, the greatest growth and amylase production were obtained with 0.5% peptone. The most appropriate metal salt for amylase production was found to be 0.02% MgS04. 7H20· Amylase was produced over a wide pH range (4.5 to 9.5 for Bacillus subtilis and 5 to 10 for Bacillus licheniformis with the maximum activity between pH 6 and 8. Amylase produci ton was greater at temperatures from 18 to 24 (room temperature) at 72 hour of cultivation. The amylases which were found to be extracellular were optimally active at 400 C and pH 5.6. Bacillus licheniformis T 31 amylase was also active at pH 8. The amylases of both organisms retained 100% activities for 1 hour at 60oC. These enzymes were stable in the pH range of 5.5-8.5. MgS04,CaC12 and BaC12 were found to stimulate amylase activity. The amylases were stable in 0.5 M NaCl with 64% -78% of their original activities being. retained after 24h. In addition to amylase, Bacillus subtilis also produced pullulanse. Using chromatographic analysis, glucose, maltose and maltotriose were detected as products of hydrolysis .